Monitoring and Calibration of Belle Electromagnetic Calorimeter

1. Monitoring and Calibration of Belle Electromagnetic Calorimeter Calor2002 conference 2002 March 25-29, Pasadena Kenkichi Miyabayashi (Nara Women’s Univ.) for Belle Calorimeter group

2. Outline • Brief review of Belle Calorimeter • Cosmic rays calibration • Bhabha, gg calibration • Non-linearity correction by p0 • Radiation level • Conclusions

3. Implemented to ensure stable detector operation. • Temperature and Humidity mon.&ctrl. Water cooling and Dry air facilities are there. 312 thermisters and 104 humitters for monitoring. Stable temp.(change less than 0.1deg.), Low humid.(<6%) • LED is impl’ted inside PreAmp. casing. Since there are enough number of methods, used only for check whether counter is alive.

4. Belle Electromagnetic Cal.(CsI) Located inside S.C. solenoid. In total, 8736 CsI(Tl) crystals (6624 in Barrel, 1152 in Fwd. Endcap and 960 in Bwd. Endcap) Covering 12<q<155° in Lab. frame. Inner radius(Barrel) = 1250mm. e+ e-

5. CsI(Tl) counter module • Equipping two PreAmps • behind two PDs(1cm 2cm), • Crystal dimension; • 5.5cm5.5cm(Front face) • -6.5cm 6.5cm(Rear face) • 30cm long(16.2X0), • Trapezoid shape. • Wrapped by Gore-Tex film and • aluminum-coated myler sheet. PreAmp. casing

6. Read out Electronics • To achieve 18-bits eq. dynamic range, • QtoT and TDC with auto range selection. • Suppress crystal hits < 0.5MeV to reduce • data size without sacrificing energy resolution.

7. Calibration The energy deposit in i-th counter(Ei) is obtained by; where TDCi=digitized signal, PEDi=pedestal of i-th ch and ei=electronics gain const., ‥obtained by daily elec. calib. run. Cosmic rays give Ci without beam (initial input). Ci absolute calibration; Bhabha, e+e-→gg by minimizing which results in the matrix inversion method.

8. Cosmic ray Calibration • The energy deposit • is predictable by • cosmic ray MC. • Can be done without • beam. • Gives good initial • inputs for Bhabha • calibration. • Innermost crystals in • Endcaps can be calib. • only by this method. • Suitable to mon. L.O. • as a func. of rad. dose.

9. Bhabha, gg Calibration Matrix inversion fairly converges! (except for inner -most crystals in Endcaps) After Bhabha calib. gg is used to carry out fine tuning; less systematic by material in front. Ci(after)/Ci(before) Crystal ID

10. Non-linearity correction by p0 • Bhabha, gg calib. • at highest E. point. • Interpolation in low • energy region needs • verification. • Mgg = { E1 E2 (1-cosa) }1/2 • p0 mass peak gives • information in low ene. • region(< 1GeV), • because EM shower is • well predicable by sim.

11. Resultant performance (by Eg>50MeV); s=12.1MeV/c2 p0(by Eg>50MeV); s=4.8MeV/c2 E. resol. for gg is 1.7%.

12. Beam background/Radiation The dark current of PDs are monitored at the bias voltage power supply. Total charge can be translated into Rad. dose. ~10rad. in barrel, ~40rad. in Endcap. (average/crystal)

13. Light output degradation Cosmic calib. without beam is a good mon. of L.O. After 3years physics runs; Crystals L.O decrease due to radiation; 1~2% in barrel, ~ 3% in Endcap. Enough Rad.-hard!

14. Conclusions • Belle CsI(Tl) cal. has been well-calibrated by various • methods; Elec. calib. run, Cosmic, Bhabha, gg and p0. • Resultant performance; • Energy resolution for e+e-gg is 1.7% • Mass resolution of neutral particles • p0 : 4.8MeV/c2 • h : 12.1MeV/c2 • L.O. decrease by the radiation damage is small. • ~3% for 40rad dose(in Endcap) • i.e. robust&stable against higher beam intensity. • So far, we have no dead counter.

15. Backup slides

16. Belle detector Optimized for B physics at Upsilon(4s) by the asymmetric e+e- collision. (8GeV e- v.s. 3.5GeV e+)

17. Shower reconstruction algorithm • Crystal hits < 0.5MeV are sparsified • by TDC readout. • Seed crystal: local max. >10MeV. • Recorded hits inside the 5by5 matrix • surrounding the seed crystal are • clustered. Seed crystal • Energy: summing up each hits. • Position: energy-weighted center of • gravity. Shower leakage and Position systematic are corrected based on simulation. Hits exceeding 0.5MeV

18. Leakage correction • Not all the shower activity • is contained in the • clustered counters. • corrected by multiplying • proper correction factor • which is Eg &  dependent • (predictable by MC).

19. Angle(Position) correcttion • Simple energy-weighted • center of gravity shows • systematic difference • from the true incident • position. • corrected by the • appropriate curve.

20. Effect of non-linearity correction Mass peak became consistent with MC as expected.

21. Performance (gg) Energy resolution for e+e-gg events. 1.7%.

22. Performance (p0) sp0(MeV/c2) 7 p0 reconstructed by energy-balanced two photons. Low energy; energy res. dominant. High energy; angle res. dominant. 6 5 4 0.1 1.0 Eg(GeV)

23. Luminosity measurement • Online lum. monitor based on Endcap Bhabha(high rate). • Offline lum. measured by barrel Bhabha, gg(less material). Online lum. Offline Bhabha lum. Offline gg lum. Offline Bhabha lum. Run.# All three methods are stably working; within 1%.